We propose to determine the arrangement of protein and glycoprotein components of the plasma membrane of the eucaryotic microorganism Dictyostelium discoideum. We will identify those proteins exposed at the extracellular face of the plasma membrane and those exposed at the cytoplasmic face and thus identify proteins confined to one membrane face or the other as well as those which completely span the membrane bilayer. We will determine whether all the carbohydrate portions of glycoproteins are confined to the extracellular membrane face. We will identify proteins in the plasma membrane which have single or multiple subunits. By these studies, we will test and expand models of plasma membrane structures which are currently based largely on work with the non-nucleated, non-viable, highly specialized human erythrocyte. As these studies become established, we will extend this analysis to plasma membranes from other stages of the developmental program in an attempt to analyze in detail the extent and nature of plasma membrane reorganization which accompanies cellular differentiation processes. Finally, we will compare the protein composition of plasma membranes with those proteins being synthesized at different developmental stages. These studies will be preliminary to investigations of the regulatory signals which control plasma membrane topography.